In 2016/2017, WRM assisted the City of Swan to remove a large number of exotic fish from Emu Lake, Ballajura, as well as assess the overall ecological health of the lake, and advise the City on the suitability of wetland habitat for native fish introductions.

The City of Swan’s local area plan for Ballajura outlines several restoration measures for the iconic Emu Lake, located in Perth’s northern suburbs, over the next five years. These include the removal of koi-carp and goldfish from the lake, followed by ongoing re-stocking with native freshwater fish, such as western pygmy perch (Nannoperca vittata). Over the spring and summer of 2016/2017, WRM field scientists completed two successful rounds of exotic fish species removal from Emu Lake. Using our brand new 4.3 metre electrofisher vessel, as well as tried-and-tested methods such as fyke and gill netting, the team was able to capture and remove a large number of invasive koi-carp (Cyprinus carpio), goldfish (Carassius auratus) and yabbies (Cherax destructor), as well as jewel cichlids (Hemichromis bimaculatus), a highly aggressive ornamental aquarium species originally from West Africa.

Feral species, such as koi-carp, goldfish, yabbies and ornamental cichlids, often released into the environment by ill-informed pet owners, can have a devastating impact on wetland habitats, by stirring up lake sediments and uprooting aquatic vegetation, leading to increased nutrient concentrations and potentially toxic algal blooms. These introduced species are usually more aggressive and breed more frequently than our native fish species, easily out-competing them for food and habitat. They also have the potential to bring exotic diseases to our native fish populations.

We hope that our studies will one day contribute to the re-introduction of native fish species to beautiful wetlands such as Emu Lake, but we face an uphill battle if populations of invasive species in urban environments are to ever be controlled. Prevention of new pest fish introductions is just as important as eradication, and requires effective public relations and education, such as the Western Australian Department of Fisheries’ “Don’t dump that fish” campaign.

If you spot a suspected feral fish species anywhere across WA, you can report it to the Department of Fisheries biosecurity team via the WA PestWatch portal